experimental studies of n* structure from meson electroproduction data

V.I.Mokeev, Cake Seminar at JLAB Theory Division November 28 2012

Experimental studies of N* structure from meson electroproduction data

V.I. Mokeev

Cake Seminar at JLAB Theory Center, November 28 2012


The 6 GeV era came to successful close in May 12’after fifteen years of running many productive world-class experiments. We are poised to continue our very successful experimental program with CLAS12. CLAS12 will be a unique worldwide facility for exploring strong interaction in the non-perturbative regime.


N* Program with CLAS• Studies of N* spectrum with a focus in the search for new baryon states strong support from recent LQCD studies, J.J.Dudek, R.G.Edwards, Phys. Rev. D85, 054016 (2012). - baryon state spectrum as rich as it was expected in quark models; employing SU(6) spin-flavor symmetry; -presence of hybrid baryons with masses above 1.9 GeV. bare N* masses were evaluated within the framework of DSEQCD: H.L.L. Roberts, et al., Few Body Syst. 51, 1 (2011): -incorporates dynamical chiral symmetry breaking; -reproduces N* state ordering. Experimental prospects , V.D.Burkert, arXiv:1209.2402 [nucl-ex] : -evaluation of pseudo scalar meson photoproduction amplitudes from combined studies of unpolarized cross sections and polarization asymmetries; -almost model independent information on N* spectrum, photo and hadronic couplings from singularities of analytical continuation of produiction amplitudes into a complex energy plane.

• N* structure from exclusive meson electroproduction data Extraction of resonance electroexcitation amplitudes (gvNN* electrocouplings) at different photon virtualities Q2. Recent review papers: I.G.Aznauryan and V.D. Burkert, Progr. Part. Nucl. Phys. 67, 1 (2012). I.G.Aznauryan et al., J.Phys. Conf. Ser. 299, 012008 (2011).


The studies of nucleon resonance (N*) structure: motivation and objectives

Our experimental program seeks to determine

gvNN* transition helicity amplitudes (electrocouplings) at photon virtualities 0.2< Q2<6.0 GeV2 with CLAS and at 4.0< Q2<12.0 GeV2 with CLAS12 detectors for most of the excited proton states through analyzing major meson electroproduction channels independently and in global multi- channel analyses.

This information needed to study the non-perturbative strong interaction which generates N* states as bound systems of quarks and gluons

The non-perturbative strong interaction represents the most important part of the Standard Model that we have yet to explore. The non-perturbative strong interaction is far more complex than the electromagnetic and weak interactions and very different in nature.


Theory support for the studies of N* structure with the CLAS12

detector


The Nature of Strong (non-perturbative) QCD regime

2

2Qln)233(

12)(2

nQ

f

s

• quark-gluon running couplings increases with distance

• anti- screening (b) takes over screening (a)

• s ~ 1 as Q2 → few GeV2(a) (b)

JLAB12

QED coupling QCD coupling

momentum transferto single quark

momentum transferto lepton

On the same momentum domain, the QCD coupling changes 500,000-times more that the QED coupling and run in the opposite direction.


Generation of dressed quarks and gluons

dressed quark

bare quark

dressing kernel

dressed gluon

bare gluondressing kernel

Dressed quarks and gluons acquire dynamical, momentum (distance) dependent masses, structure, andquark-gluon interaction amplitudes

• Quark/Gluon Confinement

• Dynamical Chiral Symmetry Breaking

Can not be described withinthe framework of pQCD!

Dressing contribution ~ (s)N /2 (N stands forthe number of interaction vertices) .Becomes dominant for the light u and d quarks and gluons as s ~ 1

Particular features of strong interaction in non-perturbative regime


Dynamical mass and structure of dressed quarks and gluons quark/gluon confinement

almost. pQCD

L.Chang et al, PRL 106, 072001 (2011)

ACM

AEM

• > 98% of dressed quark/gluon and N* masses and their dynamical structure are generated non-perturtbatively through dynamical chiral symmetry breaking (DCSB). The Higgs mechanism accounts for less than 2% of the nucleon & N* mass.

• the data from CLAS/CLAS12 will allow us to explore the nature of the dominant part of hadron mass, and will provide access to dressed quark dynamical structure.

• the momentum dependence of the dressed quark mass reflects the transition from quark/gluon confinement to pQCD .

ME=0.4 GeV

Gluon dynamical mass

S-x Quin etal., PR C84, 042202(R) (2011)


gvNN* electrocouplings as a window to strong interactions in non-perturbative region

• quark propagators are sensitive to the quark running mass M(p);

• dressed quark e.m. current is sensitive to the quark dynamical structure;

• quark interaction verticesG and X are sensitive to the quark non-perturbative interactions.

• Data on gvNN* electrocouplings at different Q2 probe momentum dependence of dynamical quark mass, structure, and non-perturbative qq-interactions.

• A key direction in exploration of quark/gluon confinement and DCSB in baryons.

Quark core contribution to gvNN* electrocouplings


Why studies of ground and excited nucleon states combined are needed?

Di-quarkJ

Ground state

P11

½+(1440) S11

½-(1535) S11

½-(1650)0+ 77%

1+ 23% 100%

0- 51% 43%

1- 49% 57%

• N* states of different quantum numbers offer complementary information on mechanisms of baryon generation from quarks and gluons.

• N* electrocouplings allow us to explore strong regime of QCD at

larger transverse distances with larger QCD than the ground state form factors.

Di-quark content of ground and N* states from DSEQCD with vector x vector interaction, C.D.Roberts et al.,AIP Conf. Proc. 1432, 309 (2012).

N* spectrum and structure from LQCD, J.J.Dudek, R.G.Edwards, Phys. Rev. D85, 054016 (2012).


Extraction of gvNN* electrocouplings from the data on exclusivemeson electroproduction off protons

γv

N N’

N*,△

A3/2, A1/2, S1/2

, h, ,..

N

, h, ,..

N’+*

• Separation of resonant/non-resonant contributions within the framework of reaction models; Breit Wigner ansatz for parameterization of resonant amplitudes; fit of gvNN* electrocouplings and hadronic parameters to the data.

• Consistent results on gvNN* electrocouplings from different meson electroproduction channels demonstrate reliable extraction of N* parameters.

Resonant amplitudes Non-resonant amplitudes

G

2

2/3

2

2/1*

2

)12(

2AAMJ

MqNr

Nr

g

g

N*’s photo-/electrocouplings gvNN* are definedat W=MN* through the N* electromagneticdecay width Gg :


CLAS data on yields of meson electroproduction reactions at Q2<4 GeV2

N* electroexcitation in meson electroproduction off protons

State Branch. Fract. to N.

Branch. Fract. to Nh

Branch.Frac.to Nππ

Δ(1232)P33

0.995

N(1440)P11

0.55-0.75 0.3-0.4

N(1520)D13

0.55-0.65 0.4-0.5

N(1535)S11

0.48±0.03 0.46±0.02

D(1620)S31

0.20-0.30 0.70-0.80

N(1650)S11

0.60-0.95 0.03-0.11 0.1-0.2

N(1685)F15

0.65-0.70 0.30-0.40

Δ(1700)D33

0.1-0.2 0.8-0.9

N(1720)P13

0.1-0.2 > 0.7

Hadronic decays of prominent N*s for W<1.8 GeV.


• Analyses of different meson electroproduction channels independently: +n and 0p channels: Unitary Isobar Model (UIM) and Fixed-t Dispresion Relations (DR) I.G.Aznauryan, Phys. Rev. C67, 015209 (2003). I.G.Aznauryan et al., CLAS Coll., Phys Rev. C80, 055203 (2009). hp channel: Extension of UIM and DR I.G.Aznauryan, Phys. Rev. C68, 065204 (2003). Data fit at W<1.6 GeV, assuming S11(1535) dominance H.Denizli et al., CLAS Coll., Phys.Rev. C76, 015204 (2007). +-p channel: Data driven JLAB-MSU meson-baryon model (JM) V.I.Mokeev, V.D.Burkert et al., Phys. Rev. C80, 045212 (2009). V.I.Mokeev et al., CLAS Coll., Phys. Rev. C86, 035203 (2012).• Global coupled-channel analyses of the CLAS/world data of N, gvN → N, hN,N, K,

KS exclusive channels: N.Suzuki, T.Sato , and T-S. H.Lee, Phys, Rev. C82, 045206 (2010).

Further developments by Argonne-Osaka Collaboration are in progress: www.jlab.org/conferences/EmNN2012/

Approaches for extraction of gvNN* electrocouplings from the CLAS data on exclusive meson electroproduction


Summary of the CLAS data on single-pion electroproduction off protons

Observablesarea, GeV2

Number of data points

dσ/dΩ(π0) 0.16-1.45

3.0-6.0398309000

dσ/dΩ(π+) 0.25-0.60

1.7-4.32558830 849

Ae(π0) , At(π0) 0.25-0.65 3981

Ae(π+) , At(π+) 0.40-0651.7 - 3.5

17303 535

Aet(π0) 0.25-0.61 1521

2Q

Number of data points >125,000, W<1.7 GeV, 0.15<Q2<6.0 GeV2 , almost complete coverage of the final state phase space. Electrocoupling extraction:

I.G.Aznauryan,V.D.Burkert et al.(CLAS Collaboration), PR C80, 055203 (2009).

Recent data extension:+n 1.6< W<2.04 GeV, 1.5<Q2<4.5 GeV2

K.Park private comm.

0n 1.1< W<1.8 GeV, 0.5<Q2<1.0 GeV2

N.Markov private comm.


The approaches for extraction of gvNN* electrocouplings from N exclusive electroproduction off protons

I. G. Aznauryan, Phys. Rev. C67, 015209 (2003), I.G.Aznauryan, V.D.Burkert, et al. (CLAS Collaboration), PRC 80 055203 (2009).

+

p

N

N

N

N

Nw,r,

Unitary Isobar Model (UIM)The Model based on fixed-t Dispersion Relations (DR)

• the real parts of 18 invariant Ball N electroproduction amplitudes are computed from their imaginary parts employing model independent fixed-t dispersion relations;

• the imaginary parts of the Ball N electroproduction amplitudes at W>1.3 GeV are dominated by resonant parts and were computed from N* parameters fit to the data.


Fits to gp→n differential cross sections and structure functions

DR

UIMDR w/o P11

DRUIMQ2=2.44 GeV2

Q2=2.05 GeV2

L=0 Legendre moments from various structure functions

ds/dW


The CLAS data on p differential cross sections and their fitwithin the framework of meson-baryon reaction model JM

full JM calc.-D++

+D0

2 directrp+D0

13(1520)

+F015(1685)

G.V.Fedotov et al, PRC 79 (2009), 0152041.30<W<1.56 GeV; 0.2<Q2<0.6 GeV2

M.Ripani et al, PRL 91 (2003), 0220021.40<W<2.30 GeV; 0.5<Q2<1.5 GeV2

V.I.Mokeev User Group Meeting June 18 2008 18

D(1232)P33, N(1520)D13, D(1600)P33, N(1680)F15

JM Model Analysis of the +-p Electroproduction

N* contribute to D and rp channels only

Major objectives: extraction of gvNN* electrocouplings and D, rp decay widths.


Developed based on approach: I.J.R.Aitchison, Nuclear Physics , A189 (1972), 417.

Off-diagonal transitions incorporated into the full resonant amplitudes of the JM model:

S11(1535) ↔ S11(1650)D13(1520) ↔ D13(1700)3/2+(1720) ↔ P13(1700)

WMMMS NNi

N i 2**

2*

1 )( GG Inverse of the JM unitarized N* propagator:N* N*

diagonal

N* N*

off-diagonal

Unitarized Breit-Wigner ansatz for resonant amplitudes

Full resonant amplitude of unitarized Breit-Wigner ansatz is consistent with restrictions imposed by a general unitarity condition, as well as with the resonant Argonne-Osaka ansatz in on-shell approximation.


Resonant /non-resonant contributions from the fit of +-p electroproduction cross sections within the JM model

W=1.51 GeV, Q2=0.38 GeV2 W=1.51 GeV, Q2=0.43 GeV2

full cross sectionswithin the JM model

resonant part non-resonant part

Reliable isolation of the resonant cross sections is achieved


NΔ Transition Form Factor – GM. Meson-baryon dressing vs Quark core contribution from EBAC-DCC/Argonne-Osaka analysis.

Within the framework of relativistic QM [B.Julia-Diaz et al., PRC 69, 035212 (2004)], the bare-core contribution is very well described by the three-quark component of wave function

One third of G*M at low Q2 is

due to contributions from meson–baryon (MB) dressing:

bare quark core

Q2=5GeV2

CLASHall A Hall

CMAMIBates

Meson-Baryoncloud

Could we observe the transition to pQCD in Q2 –range up to 14 GeV2 ?

Whether MB-dressing helps us to understand local/global parton-hadron duality?


The P11(1440) Electrocouplings from the CLAS Data

LF quark models: I.G.Aznauryan,

S. Capstick and

• Consistent values of P11(1440) electrocouplingsdetermined in independent analyses of N and +-p exclusive channels strongly support reliable electrocoupling extraction.

• The physics analyses of these results revealed the P11(1440) structure as a combined contribution of: a) quark core as a first radial excitation of the nucleon 3-quark ground state and b) meson-baryon dressing.

EBAC-DCC MB dressing (absolute values).

A1/2

S1/2

p 2012

p 2010 N

2009

B,Julia-Diaz et al., Phys. Rev. C77, 045205 (2008)

Phys. Rev . C76, 025212 (2007).

B.D.Keister, Phys.Rev.D51, 3598 (1995).


Evaluation of P11(1440) electrocouplings within Dyson-Schwinger Equation of QCD (DSEQCD)

DSEQCD.

A1/2 meson-baryon dressingEBAC-DCC (abs. values).

• Poincare-covariant, symmetry preserving DSEQCD evaluation.

• Account for quark mass/structure formation in dressing of bare quark by gluon cloud.

• Simplified contact interaction generates momentum independent quark mass.

parameterization of the EBAC-DCC bare electrocouplings.

D.J.Wilson, et al, Phys. Rev. C85, 025205 (2012).

GeVGeV

GeV

qp

mm

m

mDg

dressed

q

bare

q

GIR

G

IR

368.0007.0

8.093.04

4)( 2

2

• First evaluation from QCD of quark core contribution to P11(1440) electrocouplings.

• Evidence for substantial contributions from meson-baryon cloud in particular atQ2<1.0 GeV2.

• Evaluation with vector x vector interaction and momentum dependent quark mass function are in progress.


Transition N-P11(1440) form factors in LQCD

CLAS data

Includes the quark loops in the sea , which arecritical in order to reproduce the CLAS data at Q2<1.0 GeV2

Mπ = 390, 450, 875 MeVL box =3.0, 2.5, 2.5 f

• Exploratory LQCD results provide reasonable description of the CLAS data from the QCDLagrangian.

• Prospects for LQCD evaluation with improved projection operators, approaching physical mp in the box of appropriate size.

H.W. Lin and S.D. Cohen, arXiv:1108.2528

A1/2, S1/2 => F1*, F2

*


The D13(1520) electrocouplings from the CLAS data

A1/2S1/2

A3/2

M.Giannini/E.SantopintohCQM, Eur. Phys. J. A1,307 (1998).

MB dressing abs val. (EBAC)

• a reasonable agreement between the results from N and +-p exclusive channels.• contributions from 3 dressed quarks in the first orbital excitation and MB cloud combined.

• direct access from experimental data on A1/2 electrocoupling at Q2>2.0 GeV2 to quark core with negligible contribution from MB cloud.


Evidence for chiral symmetry breaking from Q2-evolution of the ground state and S11(1535) parity partner form factors

In chiral symmetry limit:

)(21)()(

:currentn transitio-1/2 1/2

);()()(

)(

);()()()(

2

2

2

1

2

2*2

2

2

2

2

2*1

2

1

22

1

)( QGqimMQGqqQJ

QFQGmmMQF

QFQGQQF

sgg

M,m are S11(1535) and proton masses, k= 1.79

F2, F2*

-F1, F1*

F1*, F2* p→S11(1535) form factors fromthe CLAS data

parameterization of elastic Dirac F1 andPauli F2 form factors

Evaluation of F1* and F2* startingfrom QCD within the framework ofLight Cone Sum Rule & LQCD.V.Braun et al., Phys. Rev. Lett., 103, 072001 (2009) .Update: LCSR at NLO is in progressJ.Rohrwild, priv. com.


High lying resonance electrocouplings from the p CLAS data analysis

Δ(1700)D33

A1/2

A3/2 S1/2

• the p electroproduction channel provided first preliminary results on S31(1620), S11(1650), F15(1685), D33(1700) , and P13(1720) electrocouplings of a good accuracy.

• information on electrocouplings of most N* with MN*<1.8 GeV is available and will be extended in few years up to Q2=5.0 GeV2.

N worldV.D.Burkert, et al., PRC 67,035204 (2003).

N Q2=0, CLASM.Dugger, et al., PRC 79,065206 (2009).

Preliminary

Preliminary

A1/2 S1/2

PreliminaryN(1720)P13

N CLAS from independent fitsof 3 W-intervals

A3/2


Forward Detector

CLAS12

CLAS12 supports a broad program in hadronic physics.

Plans to study excited baryons and mesons:

• Search for hybrid mesons and baryons

• Spectroscopy of Ξ* , Ω-

• N* Transition form factors at high Q2.

Central Detector


gvNN* Electrocouplings: A Unique Window into the Quark StructureMeson-Baryon Dressing

absolute meson-baryon cloud amplitudes (EBAC)

quark core contributions (constituent quark models)

D13(1520)

Data on gvNN* electrocouplings from E12-09-003 experiment (Q2 > 5 GeV2) will afford for the first time direct access to the non-perturbative strong interaction among dressed quarks, their emergence from QCD, and the subsequent N* formation.

CLAS: N and N/N combined

P11(1440)


Resonance Transitions at 12 GeV

CLAS12 projected

12 GeV experiment E12-09-003 will extend access to transition FF for all prominent N* states in the range up to Q2=12GeV2.

quar

k m

ass

(GeV

)

Electromagnetic form factors are sensitive to the running quark masses and their dynamical structure .

Probe the transition from confinement to pQCD regimes, allowing us to explore how confinement in baryons emerge from QCD and how >98 % of baryon masses are generated non-perturbatively via dynamical chiral symmetry breaking.

accessibleat 6 GeV

accessibleat 12 GeV

CLAS12

LQCDDSE


gvNN* Electrocoupling Sensitivity to Momentum Dependent Quark Mass & Structure

P11(1440) A1/2

colored point with error bars:available CLAS results on A1/2

electrocoupling of P11(1440)

CLAS12 projected

quark core contribution estimated within: LF quark model which employsmomentum dependent mass ofpointlike quark (F1=1, F2=0)I.G. Aznauryan and V.D.BurkertPhys. Rev. C85, 055202 (2012).

DSE with contact qq-interaction and momentum independent mass function

DSE expectation for QCD qq-interaction and momentum dependent mass function gvNN* electrocouplings measured at the Q2> 5.0GeV2 are sensitive to momentum

dependence of dressed quark mass and structure.

p 2012

p 2010

N2009


• Data on gvNN* electrocpouplings of most excited proton states in mass range MN* <1.8 GeV are available from analyses of the CLAS meson electroproduction

data at photon virtualitues Q2 <5.0 GeV2 from single meson and at Q2<1.5 GeV2 from double pion electroproduction channels. The files with numerical results can be requested from V.Mokeev ([email protected]).

• The CLAS results on gvNN* electrocpouplings offer new opportunity for hadron structure theory to explore how non-perturbative strong interaction generate excited proton states of different quantum numbers

• In the future (few years time scale):• - gvNN* electrocpoupling of N* states with M>1.6 GeV will become available from

N channels; - gvNN* electrocpoupling of most excited proton states in mass range up to 2.0 GeV and at photon virtualities up to 5.0 GeV2 will become available from

analysis of p electroproduction ;

Conclusions and outlook

mailto:[email protected]


Conclusions and outlook - contributions of D++, D0, +D13(1520), +F15(1685) and rp channels to nine 1-fold p cross sections can be obtained from the CLAS data in DIS area (2.0<W<3.0 GeV, 2.0<Q2<5.0 GeV2), if they can be used for extraction of transition p→N* GPD’s and/or for extending our knowledge on diagonal GPD’s from rp exclusive electroproduction; -two-body D++, D0, +D13(1520), +F15(1685) and rp cross sections in terms of CM angular distributions at different masses of unstable hadron can be obtained from p cross sections for subsequent extraction of these channel amplitudes, employing amplitude analysis methods;-resonant contributions to meson electroproduction amplitudes can be provided for the studies of global and local duality.

• The CLAS12 detector is the only foreseen worldwide facility, which will be capable to explore N* electrocouplings at largest photon virtualities ever achieved 5.0<Q2<12 GeV2. For the first time, we will be able to explore regime of quark core dominance, probe momentum dependence of dressed quark mass function in the transition from confinement to pQCD regime and to explore how >98 % of hadron mass in the Universe are generated via dynamical chiral symmetry breaking and how confinement in baryons emerges from QCD.


Back -up


Impact of the Recent LQCD studies of N* Spectrum and Structure on the N* Program with CLAS/CLAS12

J.J.Dudek, R.G.Edwards, Phys. Rev. D85, 054016 (2012).• each N* state with MN* <1.8 GeVhas partner in computed LQCD spectrum, but level ordering isnot always consistent to the data

• wave functions of the low-lying N* states dominate by 1-2 SU(6) configurations, while the wave function of high lying N*’s may contain many SU(6) configurations

• presence of hybrid-N*s with dominant contribution of hybrid components at MN*>1.9 GeV marked by

New direction in N* studies proposed in V.D.Burkert, arXiv:1203.2373 [nucl-ex]:Search for hybrid N*-states looking for: overpopulation of SU(6)-multiplet; particular behavior of gvNN* electrocouplings, which reflects presence of the hybrid component.

Should be verified by experiment !


Fixed-t Dispersion Relations for invariant Ball amplitudes (Devenish &Lyth)

Dispersion relations for 6 invariant Ball amplitudes:17 UnsubtractedDispersion Relations

1 Subtracted Dispersion Relation

γ*p→Nπ

(i=1,2,4,5,6)


Evidence for new N* states and couplings

StateN((mass)JP

PDG 2010 PDG 2012 KΛ KΣ Nγ

N(1710)1/2+ ***(not seen in

GW analysis)

*** *** ** ***

N(1880)1/2+ ** ** * **

N(1895)1/2- ** ** * ***

N(1900)3/2+ ** *** *** ** ***

N(1875)3/2- *** *** ** ***

N(2150)3/2- ** ** **

N(2000)5/2+ * *** ** * **

N(2060)5/2- *** ** ***

Bonn-Gatchina Analysis – A.V. Anisovich et al., EPJ A48, 15 (2012)Strong impact from the CLAS KY photoproduction data on the signala from new states

New states still need to be confirmed


Summary of the CLAS/Hall-C data on hp electroproduction off protons

Observables Coverage over Q2, GeV2

Coverage over W, GeV

References

ds/dW 2.4, 3.6 1.48-1.62 [1]

ds/dW 0.38-2.5 1.50-1.86 [2]

ds/dW 0.13-3.3 1.50-2.30 [3]

ds/dW 5.7,7.0 1.50-2.30 [4]

1. C.S. Armstrong et al., Phys. Rev D60, 052004 (1999).

2. R. Thompson et al., (CLAS Collaboration), Phys. Rev. Lett. 86, 1702 (2001).

3. H. Denizli et al., (CLAS Collaboration), Phys. Rev. C76, 015204 (2007).

4. M.Dalton et al., Phys. Rev. C80, 015205 (2009).


Summary of the CLAS data on KY electroproduction off protons

Observables Channel Coverage over Q2, GeV2

Coverage over W, GeV

References

Px,y,z K,KS0

0.7-5.4 1.60-2.60 [1]

Ae K 0.65-1.0 1.60-2.05 [2]

ds/dW K,KS0

0.5-2.8 1.60-2.40 [3]

Px,y,z K 0.3-1.5 1.60-2.15 [4]1. D.S. Carman et al.,(CLAS Collaboration), Phys. Rev. C79, 065205 (2009).2. R. Nasseripour et al., (CLAS Collaboration), Phys. Rev. C77, 065208 (2008).3. P. Ambrozewicz et al., (CLAS Collaboration), Phys. Rev. C75, 045203 (2007).4. D.S. Carman et al., (CLAS Collaboration), Phys. Rev. Lett. 90, 131804 (2003).

More than 85% of meson electroproduction data worldwide were obtained in experiments with the CLAS detector and available in the CLAS Physics Data Base: http://clasweb.jlab.org/physicsdb/


S11 (1535) electrocouplings and their interpretation

Analysis of pη channel assumes S1/2=0Branching ratios: βNπ = βNη = 0.45

CLAS pη

LC SR

LCQM

A1/2 (Q2) from Nπ and pη are consistent First extraction of S1/2(Q2) amplitude

CLAS pηCLAS nπ+HallC pη

• LQCD & LCSR calculations (black solid lines) by Regensburg Univ. Group reproduces • data trend at 2.0<Q2<11.0 GeV2. V.Braun et al., Phys. Rev. Lett., 103, 072001 (2009) .

Subject for our Workshop:Prospects for evaluation of gvNN*electrocouplings for other pairs of N* parity partners;access to quark distribution amplitudes in N* states of different quantum numbers.


Signals from N* states in the CLAS KY electroproduction dataD.Carman, private communication Q2=1.8 GeV2 Q2=2.6 GeV2 Q2=3.45 GeV2

W GeV

K

KS

KS

3/2 - 5/2-

(1950)

1/2 +3/2+

(1850) 1/2+3/2+

(2000)

3/2-5/2-

(2050)

)(cos

)()(}{

K

lKK

l

z

zdzdd

dd PC

LT

s

s

the structures in W-dependencies of Cl –moments at the same W-values in all Q2-bins are consistent with the contributions from resonances of spin-parities listed in the plots

reaction model(s) are neededfor extraction of N* parametersfrom KY electroproduction


Anticipated N* Electrocouplings from data on N & N electroproduction

Open circles represent projections and all other markers the available results with the 6-GeV electron beam

Examples of published and projected results obtained within 60d for three prominent excited proton states from analyses of N and N electroproduction channels. Similar results are expected for many other resonances at higher masses, e.g. S11(1650), F15(1685), D33(1700), P13(1720), …

This experiment will – for the foreseeable future – be the only experiment that can provide data on gvNN* electrocouplings for almost all well established excited proton states at the highest photon virtualities ever achieved in N* studies up to Q2 of 12 GeV2.

S11(1535)D13(1520)P11(1440)

CLAS CLAS

CLASHall C


Reaction Models for Extraction of gvNN* Electrocoupling at Q2>5.0 GeV2

• All currentl reaction models for extraction of gvNN* electrocouplings employ meson-baryon • degrees of freedom . They can be applied at Q2<5.0 GeV2, where meson-baryon mechanisms are most relevant.

• The models explicitly account for the transition from meson-baryon to quark degrees of freedom are needed for extracting of gvNN* electrocouplings from N and N electroproduction data at 5.0<Q2<12.0 GeV2 and W<2.0 GeV.

The starting point: Description of non-resonant mechanisms in +n, 0p, D, and rp electroproduction channels with the full coverage of reaction phase, including: hand-bag diagrams with GPD’s structure function from DIS studies; reggeized meson-baryon amplitudes; color dipole others……….

Most urgent need for gvNN* electrocpoupling studies with the CLAS12 !

Time scale:Should be ready by 2015, when E-12-09-003 experiment is scheduledto start the collection of N and N electroproduction data


• The contribution of D++, D0, +D13(1520), +F15(1685) and rp channels to nine 1-fold p cross sections (kind of shown in the slide #16) can be obtained in the future at 2.0<W<3.0 GeV and 2.0<Q2<5.0 GeV2

Would it be possible to use these results for extraction of transition →D, p→D13,(1520) p→F15 (1685) GPD’s and diagonal p→p GPD from rp exclusive channel?

• Two-body D++, D0, +D13(1520), +F15(1685) and rp cross section at different fixed running masses of unstable hadron can be determined from available p cross sections. Is it possible to use “data” on these two body angular distribution for reconstruction of these channel amplitudes?

For discussion

experimental studies of n* structure from meson electroproduction data

Documents

mokeev cake seminar

classtudies of n

bare n

mokeev user group meeting

studies of nucleon resonance

jlab theory division

jlab theory center

recent lqcd studies